Project Summary/Abstract Creatine Transporter Deficiency (CTD) is a metabolic disorder that occurs as a result of a mutation in the SLC6A8 gene which blocks the uptake of creatine (Cr) into the brain. This disrupts the buffering function of the phosphocreatine/creatine shuttle, which plays a key role in the regeneration of ATP. Without this shuttle, ATP homeostasis becomes dysregulated and proper cellular functions cannot be carried out, leading to a decline in cognition. Attempts at treating this disorder include supplementing with analogs of Cr or biosynthetic precursors of Cr. This has not proven to be a successful treatment option, as cerebral Cr levels remain low and cognition is not improved. The goal of our research is to better understand the effect of CTD on cellular bioenergetics, in order to aid in the development of effective therapies that ameliorate cognitive impairments. Our lab has generated a Crt knockout mouse (Crt -/y) that mirrors the symptomology of CTD patients and is therefore a useful tool for studying this metabolic disorder. We hypothesize that sustained activation of an alternate energy source, ketosis, via intake of the ketogenic diet (KD), will replenish ATP such that cellular functions are restored resulting in improved cognition. This approach would address cellular bioenergetics deficits by alternatively restoring ATP homeostasis independent of cerebral Cr transport and uptake. The central hypothesis for this study is that a KD is sufficient to ameliorate the cognitive and metabolic deficits seen in Crt -/y mice. Aim 1 will assess the effect of ketosis on the metabolic function in Crt -/y mice, while Aim 2 will determine the impact the ketosis has on cognitive function in Crt -/ymice. Taken together, the data from these aims will provide the foundation for effectual therapeutic options for CTD.